Biomass valorization via electrocatalytic carbon–carbon bond cleavage

Renewable electrocatalytic upgrading of biomass feedstocks into valuable chemicals is one of the promising strategies to relieve the pressure of traditional energy-based systems.Through electrocatalytic carbon–carbon bond cleavage of high selectivity,various functionalized molecules,such as organic acids,amides,esters,and nitriles,have great potential to be accessed from biomass.However,it has merely received finite concerns and interests in the biorefinery.This review first showcases the research progress on the electrocatalytic conversion of lipid/sugar-and lignin-derived molecules(e.g.,glycerol,mesoerythritol,xylose,glucose,1-phenylethanol,and cyclohexanol)into organic acids via specific carbon–carbon bond scission processes,with focus on disclosing reaction mechanisms,recognizing actual active species,and collecting feasible modification strategies.For the guidance of further extensive studies on biomass valorization,organic transformations via a variety of reactions,including decarboxylation,ring-opening,rearrangement,reductive hydrogenation,and carboxylation,are also disclosed for the construction of similar carbon skeletons/scaffolds.The remaining challenges,prospective applications,and future objectives in terms of biomass conversion are also proposed.This review is expected to provide references to develop renewed electrocatalytic carbon–carbon bond cleavage transformation paths/strategies for biomass upgrading.

Acidic Magnetic Biocarbon-Enabled Upgrading of Biomass-Based Hexanedione into Pyrroles

Sustainable acquisition of bioactive compounds from biomass-based platform molecules is a green alternative for existing CO_(2)-emitting fossil-fuel technologies.Herein,a core–shell magnetic biocarbon catalyst functionalized with sulfonic acid(Fe3O4@SiO_(2)@chitosan-SO_(3)H,MBC-SO_(3)H)was prepared to be efficient for the synthesis of various N-substituted pyrroles(up to 99% yield)from bio-based hexanedione and amines under mild conditions.The abundance of Bronsted acid sites in the MBC-SO_(3)H ensured smooth condensation of 2,5-hexanedione with a variety of amines to produce N-substituted pyrroles.The reaction was illustrated to follow the conventional Pall-Knorr coupling pathway,which includes three cascade reaction steps:amination,loop closure and dehydration.The prepared MBC-SO_(3)H catalyst could effectively activate 2,5-hexanedione,thus weakening the dependence of the overall conversion process on the amine nucleophilicity.The influence of different factors(e.g.,reaction temperature,time,amount of catalyst,molar ratio of substrates,and solvent type)on the reaction activity and selectivity were investigated comprehensively.Moreover,the MBC-SO_(3)H possessed excellent thermochemical stability,reusability,and easy separation due to the presence of magnetic core-shell structures.Notably,there was no activity attenuation after 5 consecutive catalytic experiments.This work demonstrates a wide range of potential applications of developing functionalized core-shell magnetic materials to construct bioactive backbones from biomass-based platform molecules.

Modified electronic structure and enhanced hydroxyl adsorption make quaternary Pt-based nanosheets efficient anode electrocatalysts for formic acid-/alcohol-air fuel cells

Surface/interface engineering of a multimetallic nanostructure with diverse electrocatalytic properties for direct liquid fuel cells is desirable yet challenging.Herein,using visible light,a class of quaternary Pt_(1)Ag_(0.1)Bi_(0.16)Te_(0.29)ultrathin nanosheets is fabricated and used as high-performance anode electrocatalysts for formic acid-/alcohol-air fuel cells.The modified electronic structure of Pt,enhanced hydroxyl adsorption,and abundant exterior defects afford Pt_(1)Ag_(0.1)Bi_(0.16)Te_(0.29)/C high intrinsic anodic electrocatalytic activity to boost the power densities of direct formic acid-/methanol-/ethanol-/ethylene glycol-/glycerol-air fuel cells,and the corresponding peak power density of Pt_(1)Ag_(0.1)Bi_(0.16)Te_(0.29)/C is respectively 129.7,142.3,105.4,124.3,and 128.0 mW cm^(-2),considerably outperforming Pt/C.Operando in situ Fourier transform infrared reflection spectroscopy reveals that formic acid oxidation on Pt_(1)Ag_(0.1)Bi_(0.16)Te_(0.29)/C occurs via a CO_(2)-free direct pathway.Density functional theory calculations show that the presence of Ag,Bi,and Te in Pt_(1)Ag_(0.1)Bi_(0.16)Te_(0.29)suppresses CO^(*)formation while optimizing dehydrogenation steps and synergistic effect and modified Pt effectively enhance H_(2)O dissociation to improve electrocatalytic performance.This synthesis strategy can be extended to 43 other types of ultrathin multimetallic nanosheets(from ternary to octonary nanosheets),and efficiently capture precious metals(i.e.,Pd,Pt,Rh,Ru,Au,and Ag)from different water sources.

Synergy of heterogeneous Co/Ni dual atoms enabling selective C-O bond scission of lignin coupling with in-situ N-functionalization

Selective cleavage of Csp^(2)-OCH_(3)bond in lignin without breaking other types of C-O bonds followed by N-functionalization is fascinating for on-purpose valorization of biomass.Here,a Co/Ni-based dual-atom catalyst CoNiDA@NC prepared by in-situ evaporation and acid-etching of metal species from tailor-made metal–organic frameworks was efficient for reductive upgrading of various lignin-derived phenols to cyclohexanols(88.5%–99.9%yields),which had ca.4 times higher reaction rate than the single-atom catalyst and was superior to state-of-the-art heterogeneous catalysts.The synergistic catalysis of Co/Ni dual atoms facilitated both hydrogen dissociation and hydrogenolysis steps,and could optimize adsorption configuration of lignin-derived methoxylated phenols to further favor the Csp^(2)-OCH_(3)cleavage,as elaborated by theoretical calculations.Notably,the CoNi_(DA)@NC catalyst was highly recyclable,and exhibited excellent demethoxylation performance(77.1%yield)in real lignin monomer mixtures.Via in-situ cascade conversion processes assisted by dual-atom catalysis,various high-value N-containing chemicals,including caprolactams and cyclohexylamines,could be produced from lignin.

Ammonia borane-enabled hydrogen transfer processes:Insights into catalytic strategies and mechanisms

Transfer hydrogenation(TH) with in situ generated hydrogen donor is of great importance in reduction reactions, and an alternative strategy to traditional hydrogenation processes involving pressurized molecular hydrogen. Ammonia borane(NH3BH3, AB) is a promising material of hydrogen storage, and it has attracted much attention in reductive organic transformations owing to its high activity, good atom economy, nontoxicity, sustainability, and ease of transport and storage. This review focuses on summarizing the recent progress of AB-mediated TH reactions of diverse substrates including nitro compounds, nitriles, imines, alkenes, alkynes, carbonyl compounds(ketones and aldehydes), carbon dioxide,and N-and O-heterocycles. Syntheses protocols(metal-containing and metal-free), the effect of reaction parameters, product distribution, and variation of reactivity are surveyed, and the mechanism of each reaction involving the action mode of AB as well as structure-activity relationships is discussed in detail. Finally, perspectives are presented to highlight the challenges and opportunities for AB-enabled TH reactions of unsaturated compounds.

Cooperative catalysis of Co single atoms and nanoparticles enables selective CAr-OCH_(3) cleavage for sustainable production of lignin-based cyclohexanols

In this work,a dual-size MOF-derived Co catalyst(0.2Co_(1-NPs)@NC)composed of single atoms(Co_(1))and highly dispersed nanoparticles(Co NPs)was prepared by in-situ Zn evaporation for the highperformance conversion of lignin-derived o-methoxyphenols(lignin oil)to cyclohexanols(up to 97%yield)via cascade demethoxylation and dearomatization.Theoretical calculations elaborated that the dual-size Co catalyst exhibited a cooperative effect in the selective demethoxylation process,in which the Co NPs could initially dissociate hydrogen at lower energies while Co1remarkably facilitated the cleavage of the C_(Ar)-OCH_(3)bond.Moreover,the intramolecular hydrogen bonds formed in the omethoxy-containing phenols were found to result in a decrease in the bond energy of the C_(Ar)-OCH_(3)bond,which was more prone to be activated by the dual-size Co sites.Notably,the pre-hydrogenated intermediate(e.g.,2-methoxycyclohexanol from guaiacol)is difficult to undergo demethoxylation,indicating that the selective C_(Ar)-OCH_(3)bond cleavage is a prerequisite for the synthesis of cyclohexanols.The 0.2Co_(1-NPs)@NC catalyst was highly recyclable with a neglect decline in activity during five consecutive cycles.This cooperative catalytic strategy based on the metal size effect opens new avenues for biomass upgrading via enhanced C-O bond cleavage of high selectivity.

Solid Acid Used as Highly Efficient Catalyst for Esterification of Free Fatty Acids with Alcohols

Anovel solid acid catalyst, which was prepared from sodium alginate (SA) and metal chlorides and characterized with XRD and FT-IR spectrometry, was used for the preparation of biodiesel via esterification reaction. The study results showed that the aluminum-alginate complex prepared in a cheap and easy way exhibited high catalytic activity, and a 92.6% conversion of methyl oleate was obtained in the presence of 4m% of catalyst dosage upon refluxing for 3h of methanol and acid mixed in a molar ratio of 10:1. It should be noted that the catalyst can be applied to the esterification reaction of fatty acids with various carbon chain length on methanol or different short chain alcohols, indicating that the catalyst is suitable for the preparation of biodiesel from waste oils with a high acid value.

Efficient catalytic conversion of carbohydrates into 5-ethoxymethylfurfural over MIL-101-based sulfated porous coordination polymers

In this work, a series of MIL-101-SO3H（x） polymeric materials were prepared and further used for the first time as efficient heterogeneous catalysts for the conversion of fructose-based carbohydrates into 5-ethoxymethylfurfural（EMF） in a renewable mixed solvent system consisting of ethanol and tetrahydrofuran（THF）. The influence of –SO3H content on the acidity as well as on the catalytic activity of the porous coordination polymers in EMF production was also studied. High EMF yields of 67.7% and 54.2% could be successively obtained from fructose and inulin in the presence of MIL-101-SO;H（100） at 130 °C for 15 h.The catalyst could be reused for five times without significant loss of its activity and the recovery process was facile and simple. This work provides a new platform by application of porous coordination polymers（PCPs） for the production of the potential liquid fuel molecule EMF from biomass in a sustainable solvent system.

Catalytic cascade acetylation-alkylation of biofuran to C_(17)diesel precursor enabled by a budget acid-switchable catalyst

Lignocellulosic biomass is a promising feedstock for the synthesis of value-added chemicals and biofuels.However,one of the biggest challenges for producing high-quality diesel fuels is the lack of sufficient carbon-chain length in biomass derivatives.In this study,a C_(17)diesel precursor 1,1,1-tris(5-methyl-2-f uryl)ethane(TEMF)with a yield of ca.70%was synthesized from the cascade acetylation-hydroxyalkyla tion/alkylation of bio-based 2-methylfuran(MF)with acetic anhydride(AA)catalyzed by acid-treated montmorillonite with enhanced acidity and improved porosity.The catalytic mechanism of the cascade reaction process was investigated over different types of acid species(Br?nsted acid and Lewis acid),and the influence of in situ formed acetic acid was also examined.A synergistic effect was observed to enable the synthesis of TEMF from the trimerization of MF with AA,in which Lewis acid and weak Br?nsted acid species mainly catalyze the acetylation and hydroxyalkylation processes,while the subsequent alkylation step is mainly catalyzed by strong Br?nsted acid.

Toward effective electrocatalytic C–N coupling for the synthesis of organic nitrogenous compounds using CO_(2)and biomass as carbon sources

Thermochemical conversion of fossil resources into fuels,chemicals,andmaterials has rapidly increased atmospheric CO_(2)levels,hindering global efforts toward achieving carbon neutrality.With the increasing push for sustainability,utilizing electrochemical technology to transform CO_(2)or biomass into value-added chemicals and to close the carbon cycle with sustainable energy sources represents a promising strategy.Expanding the scope of electrosynthesis technology is a prerequisite for the electrification of chemical manufacturing.To this end,constructing the C─N bond is considered a priority.However,a systematic review of electrocatalytic processes toward building C─N bonds using CO_(2)and biomass as carbon sources is not available.Accordingly,this review highlights the research progress in the electrosynthesis of organic nitrogen compounds from CO_(2)and biomass by C─N coupling reactions in view of catalytic materials,focusing on the enlightenment of traditional catalysis on C─N coupling and the understanding of the basis of electrochemical C─N coupling.The possibility of C─N bond in electrocatalysis is also examined from the standpoints of activation of substrates,coupling site,mechanism,and inhibition of hydrogen evolution reaction(HER).Finally,the challenges and prospects of electrocatalytic C─N coupling reactions with improved efficiency and selectivity for future development are discussed.

Cobalt nitride enabled benzimidazoles production from furyl/aryl bio-alcohols and o-nitroanilines without an external H-source

Benzimidazole derivatives have wide-spectrum biological activities and pharmacological effects,but remain challenging to be produced from biomass feedstocks.Here,we report a green hydrogen transfer strategy for the efficient one-pot production of benzimidazoles from a wide range of bio-alcohols and o-nitroanilines enabled by cobalt nitride species on hierarchically porous and recyclable nitrogen-doped carbon catalysts(Co/CN_(x)-T,T denotes the pyrolysis temperature)without using an external hydrogen source and base additive.Among the tested catalysts,Co/CN_(x)-700 exhibited superior catalytic performance,furnishing 2-substituted benzimidazoles in 65%–92%yields.Detailed mechanistic studies manifest that the coordination between Co^(2+)and N with appropriate electronic state on the porous nitrogen-doped carbon having structural defects,as well as the remarkable synergetic effect of Co/N dual sites contribute to the pronounced activity of Co/CN_(x)-700,while too high pyrolysis temperature may cause the breakage of the catalyst Co-N bond to lower down its activity.Also,it is revealed that the initial dehydrogenation of bio-alcohol and the subsequent cyclodehydrogenation are closely correlated with the hydrogenation of nitro groups.The catalytic hydrogen transfer-coupling protocol opens a new avenue for the synthesis of N-heterocyclic compounds from biomass.

Boosting alkaline hydrogen evolution performance by constructing ultrasmall Ru clusters/Na^(+),K^(+)-decorated porous carbon composites

The construction of efficient and durable electrocatalysts with highly dispersed metal clusters and hydrophilic surface for alkaline hydrogen evolution reaction(HER)remains a great challenge.Herein,we prepared hydrophilic nanocomposites of Ru clusters(~1.30 nm)anchored on Na^(+),K^(+)-decorated porous carbon(Ru/Na^(+),K^(+)-PC)through hydrothermal method and subsequent annealing treatment at 500℃.The Ru/Na^(+),K^(+)-PC exhibits ultralow overpotential of 7 mV at 10 mA·cm^(-2),mass activity of 15.7 A·mgRu^(-1)at 100 mV,and long-term durability of 20,000 cycles potential cycling and 200 h chronopotentiometric measurement with a negligible decrease in activity,much superior to benchmarked commercial Pt/C.Density functional theory based calculations show that the energy barrier of H-OH bond breaking is efficiently reduced due to the presence of Na and K ions,thus favoring the Volmer step.Furthermore,the Ru/Na^(+),K^(+)-PC effectively employs solar energy for obtaining H_(2)in both alkaline water and seawater electrolyzer.This finding provides a new strategy to construct high-performance and cost-effective alkaline HER electrocatalyst.

PtCu subnanoclusters epitaxial on octahedral PtCu/Pt skin matrix as ultrahigh stable cathode electrocatalysts for room-temperature hydrogen fuel cells

Achieving stable surface structures of metal catalysts is an extreme challenge for obtaining long-term durability and meeting industrial application requirements.We report a new class of metal catalyst,Pt-rich PtCu heteroatom subnanoclusters epitaxially grown on an octahedral PtCu alloy/Pt skin matrix(PtCu1.60),for the oxygen reduction reaction(ORR)in an acid electrolyte.The PtCu1.60/C exhibits an 8.9-fold enhanced mass activity(1.42 A·mgPt^(−1))over that of commercial Pt/C(0.16 A·mgPt^(−1)).The PtCu1.60/C exhibits 140,000 cycles durability without activity decline and surface PtCu cluster stability owing to unique structure derived from the matrix and epitaxial growth pattern,which effectively prevents the agglomeration of clusters and loss of near-surface active sites.Structure characterization and theoretical calculations confirm that Pt-rich PtCu clusters favor ORR activity and thermodynamic stability.In room-temperature polymer electrolyte membrane fuel cells,the PtCu1.60/C shows enhanced performance and delivers a power density of 154.1/318.8 mW·cm^(−2)and 100 h/50 h durability without current density decay in an air/O_(2)feedstock.

PtCu_(3) nanoalloy@porous PWO_(x) composites with oxygen container function as efficient ORR electrocatalysts advance the power density of room-temperature hydrogen-air fuel cells

It is challenging and desirable to construct Pt-based nanocomposites with oxygen storage function as efficient oxygen reduction reaction(ORR)catalysts for practical proton exchange membrane fuel cells(PEMFCs).Herein,we achieve novel porous nanocomposites of PtCu_(3) nanoalloys-embedded in the PWO_(x) matrix(PtCu_(3)@PWO_(x)),which has an oxygen container feature.The PtCu_(3)@PWO_(x)/C exhibits an ultrahigh mass activity(MA)of 3.94 A·mgPt−1 for ORR,which is 26.3 times as high as the commercial Pt/C and the highest value ever reported for PtCu-based binary system.Theoretical calculations reveal that the compressive strain and d-band center downshift of Pt intrinsically contribute to the excellent ORR performance.In H_(2)-air PEMFCs at room temperature,furthermore,the PtCu_(3)@PWO_(x)/C delivers a high power density(218.6 mW·cm^(−2)),much superior to commercial Pt/C(131.6 mW·cm^(−2)).In H_(2)-O_(2) PEMFCs,PtCu_(3)@PWO_(x)/C outputs a maximum power density of 420.1 mW·cm^(−2).This work provides an effective idea for designing oxygen-storing ORR catalysts used for practical room-temperature H_(2)-air fuel cells.

Low-coordinated surface sites make truncated Pd tetrahedrons as robust ORR electrocatalysts outperforming Pt for DMFC devices

Developing highly stable and active non-Pt oxygen reduction reaction(ORR)electrocatalysts for power generation device raises great concerns and remains a challenge.Here,we report novel truncated Pd tetrahedrons(T-Pd-Ths)enclosed by{111}facets with excellent uniformity,which have both low-coordinated surface sites and distinct lattice distortions that would induce“local strain”.In alkaline electrolyte,the T-Pd-Ths/C achieves remarkable ORR specific/mass activity(SA/MA)of 2.46 mA·cm^(−2)/1.69 A·mgPd^(−1),which is 12.3/16.9 and 10.7/14.1 times higher than commercial Pd/C and Pt/C,respectively.The T-Pd-Ths/C also exhibits high in-situ carbon monoxide(CO)tolerance and 50,000 cycles durability with an activity loss of 7.69%and morphological stability.The rotating ring-disk electrode(RRDE)measurements show that a 4-electron process occurs on T-PdThs/C.Theoretical calculations demonstrate that the low-coordinated surface sites contribute largely to the enhancement of ORR activity.In actual direct methanol fuel cell(DMFC)device,the T-Pd-Ths/C delivers superior open-circuit voltage(OCV)and peak power density(PPD)to commercial Pt/C from 25 to 80℃,and the maximum PPD can reach up to 163.7 mW·cm−2.This study demonstrates that the T-Pd-Ths/C holds promise as alternatives to Pt for ORR in DMFC device.

Interface-rich Au-doped PdBi alloy nanochains as multifunctional oxygen reduction catalysts boost the power density and durability of a direct methanol fuel cell device

The development of cathode oxygen reduction reaction(ORR)catalysts with high characteristics for practical,direct methanol fuel cells(DMFCs)has continuously increased the attention of researchers.In this work,interface-rich Au-doped PdBi(PdBiAu)branched one-dimensional(1D)alloyed nanochains assembled by sub-6.5 nm particles have been prepared,exhibiting an ORR mass activity(MA)of 6.40 A·mgPd^(−1) and long-term durability of 5,000 cycles in an alkaline medium.The MA of PdBiAu nanochains is 46 times and 80 times higher than that of commercial Pt/C(0.14 A·mgPt^(−1))and Pd/C(0.08 A·mgPd^(−1)).The MA of binary PdBi nanochains also reaches 5.71 A·mgPd^(−1).Notably,the PdBiAu nanochains exhibit high in-situ carbon monoxide poisoning resistance and high methanol tolerance.In actual DMFC device tests,the PdBiAu nanochains enhance power density of 140.1 mW·cm^(−2)(in O_(2))/112.4 mW·cm^(−2)(in air)and durability compared with PdBi nanochains and Pt/C.The analysis of the structure–function relationship indicates that the enhanced performance of PdBiAu nanochains is attributed to integrated functions of surficial defect-rich 1D chain structure,improved charge transfer capability,downshift of the d-band center of Pd,as well as the synergistic effect derived from“Pd-Bi”and/or“Pd-Au”dual active sites.